My 2-cents (and FWIW, I flew ~4000 hours between F-4's, A-10's, and F-111's).

You can do CAS with an F-16, F-15E, AC-130, B-1, and B-52. When the F-35 gets up to speed, you could do CAS with them.

The best thing about the A-10 and CAS, that was the only mission we trained to do (with maybe a little bit of SAR escort). We weren't training to shoot down MIG's, bomb bridges in downtown Baghdad, or fly nuke strike missions. The pilots are good at doing CAS.

A big advantage when comparing A-10's to F-16's (and probably to F-35's) was the ability of an A-10 to loiter. We had quite a bit of gas and we could orbit for a long time waiting for something to happen compared to the "fighters".

While bombers have even more loiter time than an A-10, it's tough to employ JDAM's if the bad guys are moving around, especially if the bad guys are close to the friendlies.

In our current "wars", the bad guys don't have much in the way of air defense. A-10's and AC-130's are perfectly survivable. That could change, but if there are lots of sophisticated SAM's, MIG's, and radar directed AAA batteries around we're probably not doing much CAS anyway.

One last thing. In the A-10, we could fly low level in some pretty marginal weather. If you're just puking off JDAM's, you can fly around at high altitude in any weather. But when the ground pounders need the pilot to put "eyes on target", you have to be below the clouds. It was sure easier flying around low level in crappy weather in a 250-300 knot A-10 than it was in a 420-540 knot F-4/F-111. You sure aren't going to take an AC-130/B-1/B-52 and go around hand flying looking for bad guys with low ceilings and low visibility.

The USAF doesn't have all the money they want for everything, and the powers that be in the USAF would sure rather have F-35's than A-10's. The A-10's are old and CAS isn't viewed as the sexiest mission the USAF does. If the USAF had their way, the A-10's would all be in the boneyard by now. Thanks, Congress!